Principal Investigator/Program Director (Last, first, middle): Kohn, Donald B. The Cell Isolation and Analysis Core (Core B) will provide two main functions for all five projects: 1. Acquisition and Isolation of stem and progenitor cells from murine and human hematopoietic tissues using antibody- mediated enrichment techniques (e.g. magnetic bead sorting) and flow cytometric sorting, and 2. Analysis of cells and tissue by flow cytometry and histology respectively. The Core will be housed at Childrens Hospital Los Angeles and run under the direction of Dr Gay Crooks. Dr Crooks has nine years experience in isolation of hematopoietic stem and progenitor cells using immunomagnetic bead and Fluorescence Activated Cell Sorting (FACS) technology and in FACS analysis of cell differentiation and gene marking. She has published extensively on the use of multiparameter FACS analysis to identify rare populations of functionally uniform hematopoietic populations and routinely uses bulk and single cell FACS sorting in her laboratory for clonal analysis of these populations. Dr Crooks has also published work using FACS analysis for assessment of gene transfer, apoptosis, cell division history, transgene expression, and retroviral binding to target cells. Dr Deborah Schofield, Associate Professor in the Pathology Department, University of Southern California and staff pathologist at CHLA, will supervise the histology portion of the Core. Dr Schofield has expertise in all aspects of the Histology service including knowledge of murine histology. 1. Acquisition and Isolation of stem and progenitor populations. 1.1 Acquisition: The Core will co-ordinate the acquisition of human cord blood and bone marrow samples for Projects 1-4. Cord blood will be acquired (without cost) through a collaboration already established with Kaiser Permanente Sunset Hospital. The Core will supply collection tubes and anticoagulant and provide the